In certain video disc systems, video information is recorded by means of geometric variations in the bottom of a smooth spiral groove on the surface of a disc record. The disc record surface includes a coating of conductive material which is preferably covered with a thin deposit of dielectric material. A signal pickup, supported at one end of a pickup arm, engages the spiral groove and includes a conductive electrode which establishes a capacitance with the conductive coating and the dielectric deposit of the disc record. When the disc record is rotated, the electrode-disc capacitance varies in response to the geometric variations in the bottom of the spiral groove. The capacitance variations are converted to electrical signal variations by suitable signal processing circuitry coupled to the pickup electrode. The output signal of the signal processing circuitry may be coupled to a conventional television receiver for reproduction. The other end of the pickup arm is releasably secured to a support member of a supporting structure of the playback system. A system of the aforementioned type is described in detail in U.S. Pat. No. 3,842,194, issued to J. K. Clemens on Oct. 15, 1974.
Video disc systems of the aforementioned type generally utilize disc records having groove densities in the order of four to eight thousand groove convolutions per inch. A typical video disc record of this type may have a groove convolution spacing in the order of 3.5 microns. The fragile walls of relatively narrow grooves of the disc record cannot be dependably relied upon to pull the weight of the pickup arm assembly, around the pickup arm pivot support, across the entire recorded surface of the disc record. Also in video disc systems utilizing variable capacitor concept, it is desirable for accurate reproduction of the prerecorded signals that the signal pickup electrode maintain a substantially constant attitude in the spiral groove. Therefore, the supporting structure includes a radial feed drive mechanism for traversing the supported end of the pickup arm in proper time relationship with the radial motion of the signal pickup tip engaged in the spiral groove so as to continuously maintain the longitudinal axis of the pickup arm substantially tangential to the spiral groove at the point of engagement. Reference may be made to the copending U.S. Application of F. R. Stave, Ser. No. 351,600, filed April 16, 1973, and entitled "VIDEO DISC PLAYBACK APPARATUS", now U.S. Pat. No. 3,870,835, for an illustration of a suitable radial feed drive mechanism for providing the indicated radial motion.
Further, in the above-mentioned type video disc systems it has been recognized that the relative motion between the disc record and the signal pickup should be maintained at a predetermined speed, and within specified tolerance limits (e.g., 450 rpm, .+-.0.01 percent), in order to obtain high fidelity of reproduction of the prerecorded signals. The predetermined speed and the specified tolerance limits are also necessary to assure that the horizontal and vertical synchronizing information is stable and within the lockup range of the deflection circuits of the television receiver. Moreover, when the prerecorded information is a color television signal with chrominance information recorded as a modulated carrier signal, the recovered signal must be stable and within the lockup range of the color processing circuits of the playback system in order to reduce color phase distortion.
The disc record/signal pickup relative speed may be maintained at the predetermined speed, and within the specified tolerance limits by rendering the pickup arm support member subject to cyclical, translatory motion along the longitudinal axis of the pickup arm in a manner that opposes deviations of the instantaneous relative speed from the predetermined speed. Illustratively, the means for imparting translatory motion to the support member may be of the type disclosed in the U.S. Pat. No. 3,711,641, issued to R. C. Palmer on Jan. 16, 1973, entitled "VELOCITY ADJUSTING SYSTEM".
Additionally, in advantageous pickup arrangements for video disc systems of the aforementioned type, the pickup arm is desirably of conductive material and enclosed in a conductive cage, so that the conductive pickup arm and the surrounding conductive cage may serve respectively as an inner and outer conductor of an electrical transmission line. The transmission line is capacity end loaded at the pickup arm supported end by a series combination of capacitances which include an air dielectric capacitor and a voltage variable capacitor (forr tuning purposes). The transmission line is also capacitor end loaded at the signal pickup end by a combination of capacitances which include the signal pickup electrode/disc record conductive coating variable capacitance. The transmission line and associated capacitances form a tuned circuit with a resonant frequency subject to variation as the signal pickup electrode/disc conductive coating capacitance varies. The tuned circuit is excited with UHF oscillations from a fixed frequency oscillator of the signal processing circuitry operating at a frequency (e.g., 915 MHz) within an ISM-allocated band. As the resonant frequency of the tuned circuit varies, the resultant UHF oscillation amplitude variations are detected by the signal processing circuitry detector to recover the prerecorded information. Reference may be made to the copending U.S. Application of D. J. Carlson, et al., Ser. No. 451,103, filed Mar. 14, 1974, and entitled "PICKUP APPARATUS FOR VIDEO DISC PLAYERS", now U.S. Pat. No. 3,872,240, for an illustration of a suitable transmission line resonant circuit arrangement and associated signal processing circuitry.
Further, in the aforementioned type video disc systems, the pickup arm and the signal pickup may desirably be treated as a replaceable unit of a size convenient to handle, whereby when the signal pickup wear calls for a replacement, the disc record player user may readily remove and replace the pickup arm/signal pickup unit without requirements for mechanical skill and manual dexterity. A replaceable unit arrangement of the aforesaid type may be desirable for several reasons. First, the replacement of the pickup arm/signal pickup unit would require no electrical wiring disconnections and connections between the signal pickup electrode and the conductive pickup arm. Second, achievement of a proper attitude for the signal pickup in its playing position may readily be established, and not left to dependence on the skill and knowledge of the user during replacement. Third, the replacement of the fragile and miniature signal pickup (e.g., the signal pickup width 2 microns, the signal pickup depth 5 microns, and the signal pickup electrode depth 0.2 microns) would be rendered practical. Reference may be made to the copending U.S. Application of M. A. Leedom, Ser. No. 522,815, filed concurrently herewith, and entitled "PICKUP ARM CARTRIDGE", for an illustration of a suitable replaceable unit.
It may be noted that the disc records having high groove densities (e.g., 4,000 to 8,000 grooves per inch) and subject to occasional flaws causing premature termination of the spiral groove. Such premature termination (commonly referred to as a "locked groove") may result in an undesired repetition of a particular groove convolution during disc record playback. It is therefore desirable to incorporate in a video disc player an apparatus suitable for relieving signal pickup from the locked groove predicament.
In certain particular applications of a video disc record system, it may be desirable to provide stop action of the displayed image. That is, to repetitively provide output signals of basically the same displayed image on an associated television monitor. Such image stop action may be desirable for allowing a viewer to observe a particular image for relatively long lengths of time. Also, in data storage systems where it may be desirable to store frames of textbook type material, the ability to linger on a particular displayed image is of special importance.
A further desirable feature for incorporation with a video disc player is the ability to provide rapid forward motion or reverse motion of the displayed image. A rapid forward function is particularly useful for quickly scanning information recorded on the video disc record. A reverse motion function may also be utilized for aiding in data retrieval and is particularly useful as a teaching aid for reviewing an instructional picture sequence recorded on the disc.
In a copending application of M. A. Leedom et al., Ser. No. 499,557, filed Aug. 22, 1974, entitled "DISC RECORD GROOVE SKIPPER", and assigned to the present assignee, an arrangement for repositioning a signal pickup from one convolution to another of a spirally grooved disc record is described. In the arrangement of said Leedom et al. application, a bimorph element is interposed between a pickup arm and a signal pickup. A pair of wires are provided for electrically connecting the bimorph element to means for generating bimorph element energizing control signals.
The present invention is concerned with a modification of the disc record groove skipper of the general form described in the aforesaid Leedom et al. application to provide a groove skipper apparatus of a modified form which may, (1) permit ready disassembly and assembly of the replaceable pickup arm unit without need for any electrical wiring disconnections and connections between the bimorph element and the control signal generating means, (2) reduce cost of replacement of the pickup arm unit by avoiding the unnecessary replacement of the bimorph element each time the pickup arm unit is replaced, (3) improve compliance of the pickup arm unit, to the arcuate motion of the pickup arm caused by the groove-riding signal pickup, by eliminating the arcuate motion of the fly leads (wires) connecting the bimorph element to the control signal generating means, and (4) reduce possible electrical interference with the playback system signal processing circuitry by remotely locating the bimorph element (and the associated wire connections) relative to the pickup-electrode/disc-record-conductive-coating signal capacitance and associated pickup circuit elements.